From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 77C0BEB64DA for ; Tue, 4 Jul 2023 20:07:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231719AbjGDUHE (ORCPT ); Tue, 4 Jul 2023 16:07:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45630 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231250AbjGDUHD (ORCPT ); Tue, 4 Jul 2023 16:07:03 -0400 Received: from mail-yw1-x1149.google.com (mail-yw1-x1149.google.com [IPv6:2607:f8b0:4864:20::1149]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4F8B718B for ; Tue, 4 Jul 2023 13:07:02 -0700 (PDT) Received: by mail-yw1-x1149.google.com with SMTP id 00721157ae682-56ff81be091so62927677b3.0 for ; Tue, 04 Jul 2023 13:07:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1688501221; x=1691093221; h=content-transfer-encoding:cc:to:from:subject:message-id :mime-version:date:from:to:cc:subject:date:message-id:reply-to; bh=r8il2W3A+Y7dZW8xauwfpOUi9D6SLUIEJNmGFcA4NVg=; b=6VCAkwu8Vj/qi03mCMziSMUtK2HemZuvC0I/OyVXR3EqfP3G6zpDUX/yE5A84wYXHs Vprk+pCbwwr5BJIsl2f7iCstULYXel5PXQjVyFU8x4ocxvsmJu/Ijw9ucU9zSExQSPVJ GjfBPz+I4GWvxMeyFmWCK+hZnrn51I2seHLCHVjcRPGORoPK3UC0L3RotkOC9Mpu7r22 63WqExhTkViW4O6Pxql2AJSPXAmeeLluTcOHO6Kga2OWz7K11pb+2XVjOc/Ovw26usyn NFE/enwZP1tGesPvIGeRCKvuC/KSspHC43PLVf8huMbGaGy2Y2IHO2VvZnoKNaEc8d3t OWjg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1688501221; x=1691093221; h=content-transfer-encoding:cc:to:from:subject:message-id :mime-version:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=r8il2W3A+Y7dZW8xauwfpOUi9D6SLUIEJNmGFcA4NVg=; b=EJAAZTqYvBxHMaTUTg1iWk/Dp+yb/sK4+rz118+HxZcCRxSZcpxtjPmQevYJmrep3o Mbk+aySGQsFfBpHUMBJXv7fXw9toBeP+SjHwJtB85rA82AnpNWRKeqIVFCLdOAXa/6hP ixsOFp8BRrkHelTpWL0HdcFHlgaHBYUBX8rFsKJ10JwxRdb18UzGKI3ldX/A80+dtFHC 3JIZtIcBzCnxPNAqKZofCo078hkcaboqx5+OHQcZG4sQ8P+LNg3zq8C0jgEJYwQbFRts kTFqmlavZ6fEr5Sykc9mUOsvrsReByMW7y/sfwb3onIKTg34HdCLZesL75xZ9RG7iAwm uzMw== X-Gm-Message-State: ABy/qLYlYtJNqXr8uMyb+J5DLNdAY7sQ+RpXyAImv13Qr8u5SrZb5+XL Ojn+92vQOa3eHXzWbab2qXdACsGEGQ8= X-Google-Smtp-Source: APBJJlEeX9skwLcSa6ScHb3JM5//3ONAkxhpQ7w9Tg9rQrPR9RX9XqSOF0TFni9TD5TubYd6ol0QzlgFmOw= X-Received: from surenb-desktop.mtv.corp.google.com ([2620:15c:211:201:9164:ef9f:8918:e2b6]) (user=surenb job=sendgmr) by 2002:a81:4109:0:b0:56f:f77c:3c7d with SMTP id o9-20020a814109000000b0056ff77c3c7dmr103135ywa.3.1688501221474; Tue, 04 Jul 2023 13:07:01 -0700 (PDT) Date: Tue, 4 Jul 2023 13:06:56 -0700 Mime-Version: 1.0 X-Mailer: git-send-email 2.41.0.255.g8b1d071c50-goog Message-ID: <20230704200656.2526715-1-surenb@google.com> Subject: [PATCH 1/1] fork: lock VMAs of the parent process when forking From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: jirislaby@kernel.org, jacobly.alt@gmail.com, holger@applied-asynchrony.com, hdegoede@redhat.com, michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org, ldufour@linux.ibm.com, paulmck@kernel.org, mingo@redhat.com, will@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, punit.agrawal@bytedance.com, lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com, chriscli@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, rppt@kernel.org, jannh@google.com, shakeelb@google.com, tatashin@google.com, edumazet@google.com, gthelen@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Suren Baghdasaryan Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When forking a child process, parent write-protects an anonymous page and COW-shares it with the child being forked using copy_present_pte(). Parent's TLB is flushed right before we drop the parent's mmap_lock in dup_mmap(). If we get a write-fault before that TLB flush in the parent, and we end up replacing that anonymous page in the parent process in do_wp_page() (because, COW-shared with the child), this might lead to some stale writable TLB entries targeting the wrong (old) page. Similar issue happened in the past with userfaultfd (see flush_tlb_page() call inside do_wp_page()). Lock VMAs of the parent process when forking a child, which prevents concurrent page faults during fork operation and avoids this issue. This fix can potentially regress some fork-heavy workloads. Kernel build time did not show noticeable regression on a 56-core machine while a stress test mapping 10000 VMAs and forking 5000 times in a tight loop shows ~5% regression. If such fork time regression is unacceptable, disabling CONFIG_PER_VMA_LOCK should restore its performance. Further optimizations are possible if this regression proves to be problematic. Suggested-by: David Hildenbrand Reported-by: Jiri Slaby Closes: https://lore.kernel.org/all/dbdef34c-3a07-5951-e1ae-e9c6e3cdf51b@ke= rnel.org/ Reported-by: Holger Hoffst=C3=A4tte Closes: https://lore.kernel.org/all/b198d649-f4bf-b971-31d0-e8433ec2a34c@ap= plied-asynchrony.com/ Reported-by: Jacob Young Closes: https://bugzilla.kernel.org/show_bug.cgi?id=3D217624 Fixes: 0bff0aaea03e ("x86/mm: try VMA lock-based page fault handling first"= ) Signed-off-by: Suren Baghdasaryan --- kernel/fork.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/fork.c b/kernel/fork.c index b85814e614a5..d2e12b6d2b18 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -686,6 +686,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *= mm, for_each_vma(old_vmi, mpnt) { struct file *file; =20 + vma_start_write(mpnt); if (mpnt->vm_flags & VM_DONTCOPY) { vm_stat_account(mm, mpnt->vm_flags, -vma_pages(mpnt)); continue; --=20 2.41.0.255.g8b1d071c50-goog